1. Field of the Invention
This invention relates to a sheet bundle folding apparatus.
This sheet bundle folding apparatus is used when for example, in an image forming apparatus such as a copying apparatus, a bundle of sheets on which image formation has been effected is to be folded in two.
2. Related Background Art
There are already known various sheet treating apparatuses for effecting the post-treatment of sheets on which image formation has been effected by an image forming apparatus such as a copying apparatus.
One of these sheet treating apparatuses binds a bundle of a predetermined number of sheets and folds the bound bundle of sheets in two.
FIG. 17 of the accompanying drawings shows the construction of a sheet treating apparatus 200 according to the prior art which effects the binding and folding work.
A sheet bundle folding apparatus for folding a bundle of sheets in two is constituted by a sheet binding device 18 for binding a bundle of sheets, folding rollers 26 and 27 and a stick-out unit 25.
A sheet on which image formation has been done discharged from an image forming apparatus, not shown, is carried into the sheet treating apparatus 200.
The sheet thus carried in is conveyed by a convey roller 17 and passes by the sheet binding device 18 and is delivered to a convey roller 22, and is conveyed until the leading end edge thereof arrives at a sheet stopper 23 waiting at a first stacking position. Then, the widthwise end portions of the sheet are trued up by sheet aligning means 24 and alignment is effected.
A similar operation is repeated for a plurality of sheets, and the plurality of sheets (a bundle of sheets) are stacked at the first stacking position. The stacked bundle of sheets are bound by the sheet binding device 18.
Thereafter, a sheet stopper 23 is moved to a second stacking position, where the bundle of sheets are folded in two. The bound bundle of sheets are stuck by the stick-out unit 25, whereby they are directed to the nip portion between the folding rollers 26 and 27 and are folded in two by the folding rollers 26 and 27, whereafter they are discharged onto a stacking tray 32 outside the apparatus by a pair of discharge rollers 30 and 31.
One folding roller 26 is movable in a direction of escape (upwardly) by an amount corresponding to the thickness of the bundle of sheets to hold the bundle of sheets between it and the other folding roller 27. As shown in FIG. 18 of the accompanying drawings, the folding roller 26 is mounted on a holding plate 98 supported on a frame 8 (FIG. 17) for pivotal movement about a support shaft 98a, and is urged against the folding roller 27 mounted (fixedly) also on the frame 8, by a spring 99.
The stick-out unit 25 is designed to be moved along a groove 8a formed in the frame 8, stick out the bundle of sheet by a stick-out plate 25a at the end thereof, and direct the bundle of sheet to the nip between the folding rollers 26 and 27.
However, the above-described sheet bundle folding apparatus according to the prior art has suffered from the inconvenience that the stick-out unit 25 cannot accurately stick the bundle of sheets in a folding position therefor.
That is, the sticking position of the stick-out unit 25 is fixed at the nip position between the rollers 26 and 27 when the upper folding roller 26 is in contact with the lower folding roller 27. The stick-out unit 25 is moved along the groove 8a so as to stick the bundle of sheets at the same nip position.
In contrast, the folding position for the bundle of sheets changes before and after the upper folding roller 26 separates from the lower folding roller 27.
The folding position for the bundle of sheets before the upper folding roller separates from the lower folding roller is the nip position between the two rollers 26 and 27 and at this time, the folding position for the bundle of sheets and the sticking position of the stick-out unit 25 are coincident with each other. However, the folding position for the bundle of sheets after the upper folding roller has separated from the lower folding roller deviates from the folding position before the upper folding roller separates from the lower folding roller and correspondingly, a deviation occurs between the actual folding position for the bundle of sheets and the sticking position of the stick-out unit 25.
This has led to the possibility that the stick-out unit 25 cannot accurately the bundle of sheets in the folding position and wrinkles or breakage may occur to the sheets.